1. Field of the Invention
The present Invention relates to a method of regenerating or reclaiming wash liquors or solutions which contain alkali, such as sodium hydroxide and/or potassium hydroxide, and which are used during the mechanical cleaning of containers, especially bottles. The wash solution can contain, as impurities, dissolved aluminum, copper, other heavy metal in the form of zinc, iron, nickel, or lead, which originate from the composition of the container, and/or carbonates which result during the mechanical cleaning, as well as organic substances which adhere to the container. The reclaiming is accomplished by adding calcium compounds to such wash solutions, and separating the thus formed precipitates from the wash solutions.
2. Description of the Prior Art
Before a reuseable empty beverage container, for example in the form of a bottle, is reused, it is mechanically washed utilizing cleansing agents which customarily contain sodium hydroxide as a cleansing aid, but can additionally or in place thereof also contain potassium hydroxide. If the empty container contains aluminum, for example as a result of aluminum-containing add-ons, such as aluminum foils, or aluminum-containing labels, this aluminum is then subjected to strong corrosion from the action of these hydroxides or lyes. This reaction between aluminum and alkali solution leads to the formation of alkali aluminate along with hydrogen. This reaction is particularly undesirable to the extent that it consumes alkali solution which is needed as cleansing agent. Depending upon the position and shifting of the equilibrium (for example when exceeding a maximum aluminum concentration), aluminum hydroxide can also be precipitated, and difficult-to-remove deposits can be formed in the cleaning machines. Under unfavorable conditions, difficult-to-remove residues can even result on the empty beverage container which is to be cleaned; with glass bottles, this can lead to so-called gray bottles.
A similar situation is encountered during the cleaning of empty beverage containers which contain copper or other heavy metals, such as zinc, iron, nickel, or lead, which also originate from the labels or the like.
Thus, the used wash solution resulting during the cleaning of empty beverage containers dissolved form, and depending upon the type of label or the like, can contain one or more of the aforementioned metals in a more or less great concentration.
As a result of carbon dioxide being pulled-in from the atmosphere and the dirty empty beverage container, alkali carbonates are also formed during the wash process by means of the alkali solutions, as a result of which cleansing agent is again consumed and deposits or precipitates can be formed.
Of course, the empty beverage container which is to be cleaned also contains organic substances which originate mainly from the residue of the beverage, and which also accumulate in the used wash solution. These substances lead to an undesirable increase of the so-called COR value (value for the chemical oxygen requirement), which represents a measurement for the degree of contamination of waste water containing organic impurities in particular. The official requirements, which continuously become stricter with regard to the permissible degree of impurities in waste water that can be supplied to the sewers or other means of removal, therefore also in this case require measures via of which such substances also at least to some extent can be separated from the used wash solution of the type presently under consideration.
In addition to the already very undesirable formation of deposits in the cleaning equipment, and possibly also in the goods which are to be cleaned, all of these reactions also have as a consequence that the wash solutions are thereby consumed relatively rapidly and become ineffective. This implies not only an unnecessarily high use of working material such as alkali solutions and energy, but also a high waste water charging with the known consequences of great environmental pollution or high costs for waste water treatment. A reduction of the waste water loading by increasing the life of the wash solution, namely by suitable measures for solution treatment and reuse of the solution while at the same time reducing the salt charge in the completely used-up wash solution which is finally supplied to the waste water sewer, would therefore include great advantages if hereby at the same time the problem of formation of undesirable deposits in the cleaning equipment also could be eliminated.
In consequence of the above described problems, a series of methods have already been proposed by means of which the aluminum-containing, more or less consumed cleaning solution that is produced during the mechanical cleaning of a reuseable empty beverage container can be continuously or intermittently treated (see, for example, German Offenlegungsschrift No. 29 20 737). Various other possibilities have been proposed for removing the aluminum dissolved in such wash solutions, for example by converting the alkali aluminate into insoluble aluminum hydroxide by means of seeding with .gamma. - aluminum hydroxide. A particularly interesting manner of removing the undesirable alkali aluminate consists in converting the dissolved alkali aluminate into insoluble calcium aluminate, and subsequently separating the latter from the wash solution using known methods, for example filtration. For this purpose, the alkali-aluminate-containing wash solution is diluted with a solution of calcium oxide which, for facilitating and improving the desired precipitation, preferably also contains a polyelectrolyte. The addition of this calcium oxide solution, and the separation of the precipitating insoluble calcium aluminate, can be carried out continuously or intermittently, with a continuous manner of operation being preferred. Together with this procedure, the dissolved carbonates, for example sodium carbonate or potassium carbonate, found in the wash solution are converted into insoluble calcium carbonate, which can then also be separated from the wash solution together with the insoluble calcium aluminates. Thus, in a closed cycle method, the undesirable aluminates and carbonates can be separated from the wash solution in the washing process. Thus the solution can be used for a longer period of time, and the problems of formation of undesirable deposits in the cleaning machines and on the cleaned containers can be practically eliminated.
However, despite disadvantages, this method has the considerable drawback that for precipitation of the alkali aluminates and alkali carbonates, which are dissolved in the wash solution, in the form of insoluble calcium salts, a solution of calcium oxide must be added. This results in a rather significant dilution of the wash solution, so that the washing strength of such a solution is continuously reduced, and, after a relatively short period of time, the washing strength thereof is totally insufficient. Parallel to this, of course, is the continuous reduction of the ability of the aluminum contained in the container labels to be dissolved. Due to the increasing dilution, after a period of time the extent of precipitation of the dissolved aluminates and carbonates is also reduced, whereby the quantity of waste water to be supplied to the sewer system becomes increasingly greater. In addition, since the wash solutions for achieving an optimum washing effect normally require a temperature of approximately 60.degree. to 80.degree. C., the solution of calcium oxide required for precipitation of insoluble calcium salts additionally must be heated up to this temperature, thus involving increasingly higher costs as the close cycle process continues.
The aforementioned drawbacks of the method of German Offenlegungsschrift No. 29 20 737, are due to the necessity for using an aqueous solution of calcium oxide, and which concern reduction of the washing capability, of the ability to dissolve aluminum, and of the precipitation, of the dissolved alkali aluminates and alkali carbonates. These drawbacks can be somewhat overcome by counteracting their cause, namely the constantly increasing dilution of the wash solution. The drawbacks are counteracted by continuously or intermittently concentrating the diluted wash solution by evaporating the excess water. However, not inconsiderable costs are connected herewith as a result of the necessary additional expense for apparatus and energy. The favorable resolving of a problem is thus diminished or even entirely eliminated by the aforementioned method. However, the method or interest from the standpoint of its solution, namely the conversion of the dissolved aluminate and carbonate contained in the wash solution in question into insoluble calcium aluminate and calcium carbonate by the use of a calcium oxide solution. The method, unfortunately, as a consequence of the aforementioned comments, has drawbacks which appear to make this method anything but economical.
It is therefore an object of the present invention to develop this method further and in such a way that full use can be made of the advantageous features, while at the same time practically eliminating the drawbacks thereof. It is a further object of the present invention that it be possible with such a method to not only separate dissolved aluminates and carbonates from the used wash solution, but also to separate other dissolved metals, especially heavy metals such as copper, zinc, iron, nickel, and/or lead. Also, here is obtained therewith additional result of a reduction of the so-called COR valve of the used solution by means of a simultaneous, at least partial co-separation of organic impurities.